[AMDGPU][GFX11] Use VGPR_32_Lo128 for VOP1,2,C

    Due to the encoding changes in GFX11, we had a hack in place that
    disables the use of VGPRs above 128. This patch removes the need for
    that hack.

    We introduce a new register class VGPR_32_Lo128 which is used for 16-bit
    operands of VOP1, VOP2, and VOPC instructions. This register class only has the
    low 128 VGPRs, but is otherwise identical to VGPR_32. Therefore, 16-bit VOP1,
    VOP2, and VOPC instructions are correctly limited to use the first 128
    VGPRs, while the other instructions can freely use all 256.

    We introduce new pseduo-instructions used on GFX11 which have the suffix
    t16 (True 16) to use the VGPR_32_Lo128 register class.

Reviewed By: foad, rampitec, #amdgpu

Differential Revision: https://reviews.llvm.org/D133723